MQTT is a messaging protocol used for machine to machine communications in Internet of Things (IoT) Applications. It uses a Pub/sub architecture, with a central broker.
Within the space we have a MQTT broker running on Acidburn, where events like door openings, sensors, and the doorbell are currently broadcast on the hacman network.
Topics within MQTT are a series of levels, separated by forward slashes /. To subscribe to multiple topics at once, wildcards can be used. + matches a single level, and # matches anything below the current level.
Topic hierarchies can be set up however the user wants, we use it in the following way:
- door/inner/# - Things involving the inner door
- door/outer/# - Things involving the outer door
- door/outer/state gets an event every time the physical door is opened or closed (payload 'opened' or 'closed')
- door/outer/opened/username gets an event every time an RFID card is used to open the door (payload is the display name set by the user opening the door)
- door/outer/doorbell gets an event every time the doorbell is pushed
- door/outer/opened/key gets an event every time the door is opened with a mechanical override key
- door/shutter/# - Things involving the shutter (Obsolete, for old space)
- sensor/shutter/# - Raw and averaged sensor readings for the shutter. Gets processed into door/shutter/opened, door/shutter/closed, and door/shutter/status messages. (Obsolete, for old space)
- sensor/temp/+/reading - Temperature readings in degrees Celsius.
- wifi/clients - Number of clients connected to the unifi wireless access point.
- lights/beacon - Controls the beacon (publish to this the number of milliseconds you would like the beacon to be on for)
Subscribing to messages on linux / raspberry pi
To install the mosquitto client
sudo apt-get install mosquitto-clients
To view the inner door being opened & closed, and by who
mosquitto_sub -h acidburn -t 'door/inner/#' -v
Note that # is used as a wildcard, and will match anything after the point it is posted. To view everything on the network:
mosquitto_sub -h acidburn -t '#' -v
Subscribing to messages within python
First you'll need to install the python mqtt libraries:
sudo apt-get install python-mosquitto
Then the following code can be used to read messages on the MQTT network:
#!/usr/bin/python import mosquitto def on_message(mosq, obj, msg): if msg.topic == 'door/outer/opened/username': print("%s opened the outer door." % msg.payload) elif msg.topic == 'door/outer/buzzer': print('Buzzer') elif msg.topic == 'door/outer/invalidcard': print("Unknown card at outer door.") mqttc = mosquitto.Mosquitto("mqtt2bot") # The name of your client, probably should be unique mqttc.connect("acidburn") # the broker to connect to mqttc.subscribe("door/outer/#") # you can repeat this line multiple times to subscribe to additional topics mqttc.on_message = on_message # function to run when message is received while mqttc.loop() == 0: pass